(1) Field of the Invention
The present invention relates to a method and apparatus for scheduling packets in a cellular system where directional gain of base station is controlled in downlink communication.
(2) Description of the Related Art
In Japanese Unexamined Patent Publication No. 2003-110486 (Patent document 1), a radio channel scheduling method that can be applied for a smart antenna base station capable of concurrent communication with a plurality of mobile-stations is disclosed. In this prior art, downlink signal multiplexing transmission is performed on spatially multiplexed channels that are allocated to mobile communication apparatuses (hereinafter referred to as “mobile apparatuses”) in descending order of the quality of communication with each mobile apparatus. Interferences occurring due to spatial multiplexing are suppressed by NULLs generated by the smart antenna. A feature of this method is dispensing with an intra-cell handover of a mobile apparatus by virtue of a varying directional gain pattern of array antennas responsive to mobile apparatus moving. This feature indicates that the directional gain pattern is frequently updated for mobile apparatus tracking.
In actual downlink communication, it is thought that a positional relationship between a mobile apparatus to be a destination of a transmission signal and another mobile apparatus for which the transmission signal brings about interference is varying and, consequently, the beam and NULL orientation of the directional gain pattern must be updated frequently. For a base station, updating the directional gain patterns for all users residing in its cell imposes a great computational burden. This poses a problem in which the frequency of directional gain pattern updates is not sufficient to follow a change in the propagation environment. This problem of prior art can be solved to a certain extent by providing the base station with a capability of outputting fixed directional gain patterns, thus dispensing with computation for directional gain pattern updates.